Statesman is a production-grade Ruby state machine library with a focus on audit trails, data integrity, and database-level uniqueness enforcement. The core is the `Statesman::Machine` module, which provides a declarative DSL (states, transitions, guards, before/after callbacks) and is mixed into a machine class per model. State transitions are persisted as separate transition records (via a pluggable storage adapter), enabling full history and metadata tracking. The library ships with two adapters: an in-memory adapter for testing and an ActiveRecord adapter that uses unique indexes on `sort_key` and `most_recent` columns to prevent duplicate transitions and provide efficient current-state queries. It includes query scopes (`in_state`, `not_in_state`) for ActiveRecord models, a denormalised cached-current-state feature via `ConfigureCachedCurrentState`, and a type-safe variant of the query module for Sorbet compatibility. The codebase is highly modular, well-tested (over 130 spec files across multiple database backends), and follows modern Ruby and Rails best practices. It is maintained by GoCardless and supports Ruby 3.3–4.0 and Rails 7.2–8.1.